1. SDW2005 - Marco Sirianni Marco Sirianni (ESA/STScI) Max Mutchler (STSci) Radiation Damage in HST Detectors

2. SDW2005 - Marco Sirianni Detectors on HST CCD:(16+2) WFPC 8 3.5 yr WFPC2 4 12 yr STIS 1 7 yr ACS 3 3 yr WFC3 2 0 yr IR: (3+1)) NICMOS 3 8 yr WFC3 1 0 yr UV-MCP: (3+1)) STIS 2 7 yr ACS 1 3 yr COS 1 0 yr 1990 : WFC +FOC+FOS +GHRS+HSP 1993 : WFPC2 1997 : STIS + NICMOS 2002 : ACS ????: WFC3 +COS HST Instruments:

3. SDW2005 - Marco Sirianni CCDs on HST ACS/WFC FPA: 2x SiTe 4048x2096 Thinned Backside CCDs 15  m pixel size - MPP (integration only) Site VIS-AR Coating - 4 amps readout T = - 77 °C 3 m minichannel WFC-1 A B WFC-2 C D ACS/HRC FPA: 1x SiTe 1024x1024 Thinned Backside CCDs 21  m pixel size - MPP - Site NUV AR Coating 1 amp readout T = - 81 °C 3 m minichannel STIS FPA: Same as HRC, different AR coating T = - 83 °C WFPC2 FPA: 4x Loral 800x800 Thick Frontside CCDs 15  m pixel size - MPP 1 amp readout T = - 88 °C

4. SDW2005 - Marco Sirianni HST Radiation Environment LEO- alt. ~580 Km, incl. 28.41 - 14.99 rev/day ~ 7/9 orbits/day are SAA free ~ 6/8 orbits/day are SAA impacted LEO are quite shielded orbits… still

5. SDW2005 - Marco Sirianni Radiation Damage MPP devices are mainly sensitive to “displacement damage” Vacancies migrate until a stable configuration is reached; mainly: P-V centers V-O centers V-V centers Any new energy level in the bandgap acts as emission/trapping site Direct impact on: - Dark Current increase - hot pixels ( Field-enhanced dark spikes ) - CTE degradation

6. SDW2005 - Marco Sirianni Single Event effect On June 2003 one of the four ACS/WFC amplifier showed a jump in read noise ~ 1 e- rms in amplitude. The change occurred during a SAA transit and stabilized to +0.6 e- after few anneal cycles. STIS suffered of a similar problem ~ six months before The failure of the side-1 electronics.

7. SDW2005 - Marco Sirianni Dark Current variation WFC - 76 C + 1.8 e-/pix/hr per year HRC - 81 C + 2.1 e-/pix/hr per year As expected the dark rate increases linearly with time

8. SDW2005 - Marco Sirianni Dark Current comparison Side-2 May 2001 Dec 1999 21.6 14.4 7.2 e-/pix/hr STIS WFCHRCSTISWFPC2WF3 Predicted (rad. Test) 1.5 (-81 C)n.a 1.4 (-83 C) Observed1.82.1 3.3 (side 1) 2.2 (side 2) 2.0 (0-5 yr) ~ 0 after Temp.-77 C-81 C-83 C / (< -83 C)-88 C Dark rate increase: e-/pix/hr/yr

9. SDW2005 - Marco Sirianni Hot Pixels ACS HRC Pre flight dark frame - selected 256x256 pix region

10. SDW2005 - Marco Sirianni Hot Pixels ACS WFC Pre Flight 1 Yr 2 Yr 3 Yr

11. SDW2005 - Marco Sirianni Hot Pixels ACS WFC 0,1,2,3 yrs Field enhanced dark spikes

12. SDW2005 - Marco Sirianni Annealing of defects In order to remove contamination from the detector windows WFPC2 is heated once a month to +22 C It has been noticed a reduction of hot pixels after the CCD warm-up (up to 80%) All known traps anneal at much higher temperature (150-320 C) STIS and ACS also warm up the CCDs once a month to anneal hot pixels.

13. SDW2005 - Marco Sirianni Hot pixel annealing Anneal day Daily Hot Pixel growth Permanent Hot pixels growth Annealing rate (A - B) / ( A - C) A B C Annealing Rate : constant with time depends on the threshold same rate for 24,12,6hr soak same rate at -10 C

14. SDW2005 - Marco Sirianni Annealing comparison InstrumentTemp (CCD/ann.) Threshold (e-/pix/sec) Anneal rateSource STIS-83 / +5> 0.1~ 80 % ~ 75 % Hayes et al.1998 Kim Quijano et al. 2003 WFPC2-88 / +22> 0.02 variable ~ 80 %Koekemoer et al. 2003 WFC3 ground -83 / +30>0.01 >0.04 ~ 80 % ~ 97 % Polidan et al. 2004

15. SDW2005 - Marco Sirianni Life of a hot pixels

16. SDW2005 - Marco Sirianni Permanent hot pixelsWFC years %

17. SDW2005 - Marco Sirianni Permanent hot pixels.. SIDE2 > 0.1 > 1.0 STIS

18. SDW2005 - Marco Sirianni Permanent hot pixels.. Threshold e-/pix/sec WFCHRCSTISWFPC2 temp- 77 C - 80 C- 83 C- 88 C Dark curr.0.0030.0040.0060.008 > 0.021.601.542.99(0.30--0.11) >0.040.780.52 >0.060.460.29 >0.080.300.21 >0.100.230.170.36 >10.030.020.08 Permanent hot pixel growth (% of total number of pixels / year)

19. SDW2005 - Marco Sirianni Annealing lesson learned We still do not why ~0-20 C annealing is effective Only field-enhanced hot pixels are effected, there is no measurable impact on the uniform dark rate. The anneal rate depends on the dark rate of the pixel 24, 12, or 6 hr at +20 give the same annealing rate The same improvement is seen at -10 C (24-48hr) Evidence of reverse annealing Compete anneal is rare

20. SDW2005 - Marco Sirianni CTE monitoring Different temperature (from -76 C to -88 C) different clock rate (parallel clock rate from 20 to 60 Hz) different shielding (different trap population) WFPC2/STIS/ACS: empirical correction for point source photometry: –Measurement of charge loss as a function of signal - position - background and epoch ACS: EPER and FPR (only serial for WFC) –Every six months at several signal levels –Every month at the Fe 55 level (1620e-)

21. SDW2005 - Marco Sirianni CTE measurement We can investigate CTE degradation as a function of time/signal level. Ex: WFC -A EPER And predict the impact of science data in the next few years

22. SDW2005 - Marco Sirianni CTE trend At all signal levels CTE degradation is linear with fluence WFC PARALLEL EPER

23. SDW2005 - Marco Sirianni Single case: –Signal 1620e- –Low backg. 1e- –1000 transfers  mag converted into CTE CTE Degradation rate Eper TEST (ACS): –Signal 1620e-

24. SDW2005 - Marco Sirianni Conclusion In 15 years more 22 detectors have flown on HST Different architectures in the same radiative environment Unique possibility: –To try to understand what is really going –To provide information for the development/operation of future space detectors Huge archive but data collection and analysis did not followed any standard.

25. SDW2005 - Marco Sirianni Conclusions We have started with CCDs analysis Dark rate increase and Hot pixel generation is quite well understood - they are a concern, but not an issue. CTE is an issue, little mitigation is possible WFPC2 “saturation” to radiation is a “mystery” We have better understanding of annealing effectiveness, but we still do not why it occurs We will post the data of the analysis on a dedicated web page at STScI.